Imaging technique could improve early cancer diagnosis and guided surgery.

Researchers have designed and used a new class of light-emitting particles as molecular imaging agents, illuminating tissue like lymph nodes and tumors in mice. The new particles could improve cancer detection and guidance during surgery due to their advantages over other visualization techniques.

Researchers use a variety of techniques for visualizing the insides of living bodies using light, and most of these techniques require shining a light on the tissues during imaging. This light excites fluorescent compounds and causes them to release light of their own, which sensors can pick up and use to form an image. But this process can also induce the natural emission of light by biological tissues, which affects the image quality.

Afterglow optical agents, which emit light long after removal of the light source, are a promising alternative due to the slow release of photons once they have been heated up. However, afterglow imaging has been limited by its reliance on inorganic nanoparticles made of toxic metals.

Now, researchers have developed new afterglow optical agents that can emit long-lasting light after the cessation of light excitation.

The new afterglow optical agents belong to a class of photonic nanomaterials called semiconducting polymer nanoparticles, or SPNs, which are completely organic and contain biologically benign ingredients. In the new study, researchers found that the afterglow of these SPNs allows faster and more sensitive imaging of lymph nodes and tumors than traditional imaging methods. The afterglow intensity of SPNs is more than a hundredfold brighter than that of inorganic afterglow agents, bright enough to be detectable through the body of a live mouse.

The researchers also developed an SPN afterglow probe for early detection of drug-induced liver injury in living mice.

The sensitivity of the SPN agents—up to 100 times higher than that for traditional near-infrared fluorescence imaging—suggests great promise as a research and medical imaging tool, the researchers reported this month in Nature Biotechnology.